The invention relates to a cooking vessel with a frying fat heating device for a deep frying appliance for the ‘floating’ frying of food portions and luxury foodstuffs.
By ‘floating frying’ is meant the preparation of food or other luxury items (in the following referred to simply as ‘food’), characterised in that the food is cooked in hot deep fat, ie. appropriately cooked through for consumption. For this type of food preparation, the term ‘deep frying’, and for equipment for deep frying the term ‘deep fat frier’, have become accepted, and these are used in the presentation of the invention. Deep fat friers are used in particular for the preparation of bulk items which are prepared in the form of equally sized strips.
A bulk item of the type described, often intended for consumption, is potatoes which are prepared for consumption by deep frying. Such bulk items are generally known under the term ‘chip portions’.
Equipment for the production of chip portions is established which produces the latter from a raw or pre-cooked bulk material, manually or automatically. The established automatic equipment here essentially comprises a storage container for uncooked chips and a cooking vessel (in the following also referred to as a deep frying drum), whereby the storage container is connected to the deep frying drum by means of a pipe connection.
A scooping device operating in the storage container forms a pile of the pre-determined quantity and feeds this into the pipe which conveys the bulk into the deep frying drum. In the deep frying drum, the bulk is cooked through in hot oil, and then carried out of the deep frying drum.
A turning element turns in the deep frying drum containing the liquid frying fat, and said turning element comprises radially projecting rakes around its circumference, positioned at equal distances around said circumference, which convey the bulk material through the hot frying fat for cooking and then carry it out of the appliance. In so doing, the frying fat becomes stale, and so must be changed periodically. It is changed by means of a discharge cock which carries the stale frying fat out of the deep frying drum, whereby the deep frying drum is then filled back up again on its front side. The appliance must be cleaned before refilling, and this takes a lot of time and effort in order to keep the equipment in a hygienically sound state. It is the frequency of the time and effort taken to do this as well as the cost of the frying fat to be changed which determines the cost-effectiveness of a deep frying appliance.
The frequency of the changes of frying fat depends greatly upon the type of heating, ie. heating up, and the homogeneity of the heat distribution in the frying fat. Deep frying drums are known with direct and with indirect frying fat heating. Direct frying fat heating means that the heating is by means of heating elements located in the frying fat (heating within the deep frying drum), and indirect heating means that the frying fat is heated by means of a cyclical heating device outside of the deep frying drum (heating outside of the deep frying drum). Heating in a vessel by warming the vessel walls by means of heat sources which act upon the outer surface of the vessel walls also falls into the category of indirect heating.
With the first case of indirect heating, the frying fat or deep frying oil is pumped out of the drum, conveyed through the cyclical heating device, and subsequently pumped back into the drum. There are disadvantages associated with these types of heating. The direct heating brings about convection in the liquid frying fat, ie. so-called equalisation currents intended to distribute heat evenly through the frying fat. If a portion of material to be cooked is introduced into the frying fat, the convection and heat distribution is easily disrupted, and the items to be cooked are not cooked through sufficiently. These problems relating to convection also occur with indirect heating in a container by means of heat sources which act upon the vessel from outside. In order to counter these, heating temperatures for the frying fat are set higher than actually required, ie. at an inflated level. It is this inflated heating output which contributes significantly to the deterioration of the frying fat, and so also to increased frequency of the changes. With the indirect heating method by means of a so-called cyclical heating device, the method used is a circulation process.
Because a pump sucks frying fat out of a cooking drum or a cooking vessel, feeds it through the heating device and conveys it back into the cooking drum, the circulating quantity of frying fat brings about a certain current in the frying fat which gives rise to problems of convection in the background. In the pumps, on the other hand, the liquid frying fats are subjected to mechanical forces which lead to premature deterioration, and so also to frequent changes of the frying fat.